LONDON, Jan 16 (Reuters) - A helicopter crashed into a craneon top of one of Europe's tallest residential blocks in centralLondon on Wednesday, killing two people as it burst into flamesand threw plumes of smoke into the foggy air.

Police said there was nothing to indicate that the crash onthe south bank of the River Thames was linked to an attack onLondon, where 52 commuters were killed in rush hour suicidebombings in 2005.

"There was a really loud bang," said Julie Marsden, whoworks in an office building near the crash site which is closeto landmarks such as the headquarters of Britain's MI6international intelligence agency and the Houses of Parliament.

London's police Commissioner Bernard Hogan-Howe said therewere 11 casualties including two dead and one criticallyinjured. The fire service said it had rescued a man from aburning car near Vauxhall train station, a major commuterstation on the south side of London, shortly after 0800 GMT.

Hogan-Howe said the helicopter had been diverted to ahelipad in Battersea, near the crash site. He declined to givefurther information until relatives had been informed.

"We're treating it as a major incident," he told the LondonAssembly.

Rezart Islami, 27, a construction worker from Kosovo who hadbeen on a nearby site, said he saw the helicopter flying fast upthe river before it smashed into the crane, span out of controland hit the ground bursting into flames some seconds later.

The crane fell and hit two cars. "I was shocked, it wasspinning around and lost control," he told Reuters.

CRANE CRASH

Another witness, Edmir Pishtar, who was in a van outside thebuilding site, said he saw half the crane crash down and cutinto two cars on the road. He later spoke to the crane operatorwho was about to get inside the crane cab.

"He was literally shaking because he was getting ready toclimb into the crane and he was late."

The circular block - The Tower, One St George Wharf - isdescribed on its website as the epitome of luxury London living,with 360-degree views across the capital and over the Houses ofParliament.

Builder Brookfield Multiplex said the tower, which is notoccupied, is 52 floors or 185 metres (200 yards) high and has212 luxury apartments. Media reports in recent years havesuggested the Penthouse apartments could go for as much as 50million pounds ($80 million).

A Reuters correspondent at the scene said tangled bits ofcrane could be seen hanging off the side of the tower, the topof which was still shrouded by low cloud. TV footage showedflaming wreckage strewn across a road.

"Fortunately for us we have done a full headcount and thereare no injuries or fatalities among anyone on the site," saidTony Pidgley, chairman of the tower's developer Berkeley Group.

"The crane driver normally starts at eight o'clock butunusually, today of all days, was late."

He said it was too early to speculate on the cause of thecrash but helicopters should normally fly 500 feet (150metres)above tall structures.

Police were questioning witnesses in the area and dozens ofemergency vehicles were in attendance, Reuters reporters said.London train and underground train services were working asusual.